Photoexcited Carrier Lifetime and Refractive Nonlinearity in Direct and Indirect Band Gap Crystals on the Z-Scan Technique

The Photoexcited carrier lifetime and peak to valley transmission difference (Tp-v) in direct and indirect band gap crystals has been investigated by the use of single beam open and closed aperture z-scan technique using frequency doubled Nd:YAG laser. The peak to valley transmission difference (Tp-v) is found to be of the order of 10-2 in case of direct band gap crystals and of the order of 10-3 in case of indirect band gap crystals. The carrier life time is found to be in nanoseconds range in case of direct band gap crystals and picoseconds range in case of indirect band gap crystals. Lower value of and (Tp-v) in case of indirect band gap crystals can be attributed to the reduction in the value of carrier density (N) and small value of nonlinear phase shift, respectively.